Thermal behavior study of palladium(II) complexes containing the iminic ligand N,N′-bis(3,4-dimethoxybenzaldehyde) ethane-1,2-diamine

Article abstract of DOI:10.1007/s10973-018-7429-y

This study describes the synthesis, characterization and thermal behavior study of the Schiff base N,N′-bis(3,4-dimethoxybenzaldehyde)ethane-1,2-diamine (C.1) and four new compounds of palladium(II) N,N-chelate coordination, with the general formula [Pd(X₁)(X₂)(3,4dm-1,2am)] where 3,4dm-1,2am=N,N′-bis(3,4-dimethoxybenzaldehyde)ethane-1,2-diamine, X₁ = X₂ = Cl^? (C.2), X₁ = X₂ = Cl^? and Br^? (C.3), X₁ = X₂ = N₃^? (C.4) and X₁ = X₂ = NCO^? (C.5). The compounds were characterized by elemental analysis, infrared vibrational spectroscopy (IR) and nuclear magnetic resonance (NMR) ¹H and ¹³C. The TG/DTA curves showed that the thermal decomposition of the C2–C.5 complexes occurred in steps that involve the removal of both inorganic and organic ligand, and palladium oxidation steps forming palladium(II) oxide followed by the reduction of PdO into Pd(0), this being the constituent of the residual mass observed at the end of the TG curves, which have values consistent with the expected ones. The formed compounds can be ordered according to thermal stability considering the initial decomposition temperature (C.5 > C.2 > C.3 > C.4).

Full text of DOI:10.1007/s10973-018-7429-y

Journal of Thermal Analysis and Calorimetry
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Thermal behavior study of palladium(II) complexes containing
the iminic ligand N,N0-bis(3,4-dimethoxybenzaldehyde) ethane-1,2-
diamine
T. T. Xavier1 E. P. de Gois1 L. E. Sarto2 E. T. de Almeida1
•
•
•
Received: 30 November 2017 / Accepted: 27 May 2018
´
´
Ó Akademiai Kiado, Budapest, Hungary 2018
Abstract
This study describes the synthesis, characterization and thermal behavior study of the Schiff base N,N0-bis(3,4-
dimethoxybenzaldehyde)ethane-1,2-diamine (C.1) and four new compounds of palladium(II) N,N-chelate coordination,
with the general formula [Pd(X1)(X2)(3,4dm-1,2am)] where 3,4dm-1,2am=N,N0-bis(3,4-dimethoxybenzaldehyde)ethane-
1,2-diamine, X1 = X2 = Cl- (C.2), X1 = X2 = Cl- and Br- (C.3), X1 = X2 = N3- (C.4) and X1 = X2 = NCO- (C.5). The
compounds were characterized by elemental analysis, infrared vibrational spectroscopy (IR) and nuclear magnetic reso-
nance (NMR) 1H and 13C. The TG/DTA curves showed that the thermal decomposition of the C2–C.5 complexes occurred
in steps that involve the removal of both inorganic and organic ligand, and palladium oxidation steps forming palladium(II)
oxide followed by the reduction of PdO into Pd(0), this being the constituent of the residual mass observed at the end of the
TG curves, which have values consistent with the expected ones. The formed compounds can be ordered according to
thermal stability considering the initial decomposition temperature (C.5 > C.2 [ C.3 > C.4).
Keywords Pd(II) complexes Á Iminic ligand Á IR and NMR spectroscopy Á TG–DTA
Introduction
As a study material, we have palladium(II) compounds,
first synthesizing the organic ligand in order to turn the
action of this metal ion more specific. Palladium(II) com-
pounds show ligand-exchange kinetics 105 times greater
than the platinum(II) analogous, which may facilitate the
hydrolysis of the leaving groups that dissociate readily in
solution, before the complex reaches the pharmacological
target. To overcome their high lability, chelating ligands
have been used to afford high thermodynamically
stable and kinetically inert palladium(II) complexes
[10, 11]. Therefore, it is extremely important to search for
ligands that optimize its performance. The N,N0-bis(3,4-
For some time, transition metal complexes, especially
cisplatin, have been investigated due to their antineoplastic
and trypanocidal activities [1]. There are several studies in
the literature that seek to exploit the properties of palla-
dium complexes, such as cancer cells anti-proliferative
activity [2], anti-inflammatory activity [3], bactericidal
activity [4, 5] applications in catalytic processes [6, 7],
nanotechnology [8] and nucleation studies [9].
dimethoxybenzaldehyde)ethane-1,2-diamine
(3,4dm-
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10973-018-7429-y) contains
supplementary material, which is available to authorized
users.
1,2am) C.1 ligand is a Schiff base and has its synthesis and
characterization reported in literature [12–14]. We inves-
tigated the thermal behavior of a new series of coordination
compounds [Pd(Cl)2(3,4dm-1,2am)] C.2, [PdBrCl(3,4dm-
& E. T. de Almeida
tonon@unifal-mg.edu.br
1,2am)]
C.3,
[Pd(N3)2(3,4dm-1,2am)]
C.4
and
[Pd(NCO)2(3,4dm-1,2am)] C.5. The compounds were
characterized by elemental and thermogravimetric analy-
ses, as well as infrared (IR) and nuclear magnetic reso-
1
´
Instituto de Quımica – IQ, Universidade Federal de Alfenas -
UNIFAL-MG, Alfenas, MG 37130-001, Brazil
2
ˆ
1
nance (NMR) spectroscopies 13C and H.
Instituto Federal de Educac¸a
˜o Ciencia e Tecnologia do Sul de
Minas Gerais – IFSULDEMINAS, Machado, MG 37750-000,
Brazil
123

T. T. Xavier et al.
Synthesis of C.3, C.4 and C.5
Experimental
For the C.3–C.5 compounds, the same atmosphere condi-
tions were followed. To stirred dichloromethane
Instrumentation
a
(30.0 mL) solution of C.2 (about: 0.300 g; 0.56 mmol) was
added (about 1.12 mmol) the corresponding halide/pseu-
dohalide salt (KBr, NaN3 and KCNO, respectively). After
magnetic stirring of mixture for 2 h, the solvent was
evaporated and the C.3–C.5 compounds were precipitated
by adding pentane. The precipitate was separated by fil-
tration, washed with ethyl ether and dried in vacuum. The
yields were 53% (for C.3), 60% (for C.4) and 72% (for
C.5).
Elemental analysis of carbon, nitrogen and hydrogen was
performed using a Leco Instruments Ltda, model TruSpec
CHNS-O instrument. Infrared spectra were recorded as
KBr pellets on a Shimadzu-IR-Prestige-21 spectropho-
tometer in the spectral range 400–4000 cm-1. NMR
spectra were recorded on a Bruker DPX-300 spectrometer
operating at 300 MHz (1H) and 75 MHz (13C), using
CDCl3 as solvent for C.1 and C.4 or DMSO-d6 for C.2, C.3
and C.5 for dissolution of samples. The melting point (mp),
C.1, or decomposition temperatures, C.2–C.5, were
obtained using the MARTE (PFM II) equipment. The
curves of thermogravimetric analysis (TG) and differential
thermal analysis (DTA) were obtained from TA Instru-
ments equipment-Q 600, under dry air synthetic or nitrogen
flow (100 mL min-1), mass sample approximately 10 mg,
alumina crucible and heating rate of 20 K min-1 from
room temperature to 1373 K. The reference substance was
pure a-alumina in DTA measurements. The patterns of
powder X-ray diffraction (XRD) were obtained by Rigaku
Ultima IX equipment using KaCu wavelength
Results and discussion
The analytical results confirmed the proposed formulae for
the synthesized compounds. The results of the analyses are
presented in Table 1. The proposed structures for the C.1–
C.5 compounds are shown in Fig. 1.
Infrared spectra
˚
The IR spectrum of synthesized ligand C.1 exhibits the
m(N=C) band at 1637 cm-1, indicating their formation.
Compared with the spectrum of the starting primary amine,
the absence of the bands corresponding to the characteristic
(k = 1.5418 A) setting of 34 kV and 20 mA.
Synthesis of Schiff base C.1
asymmetric
(* 3300 cm-1
)
and
symmetric
A solution of ethylenediamine (0.80 mL; 11.84 mmol) in
methanol (10.0 mL) was added to a solution of 3,4-
dimethoxybenzaldehyde (3.7257 g; 22.42 mmol) in
methanol (30.0 mL). The mixture was stirred at room
temperature (approximately 298 K) for 1 h. The white
precipitate was separated by filtration, washed with water,
ethyl ether and dried in vacuum. Yield 92%.
(* 3200 cm-1) stretching (N–H) bond is observed. Fur-
thermore, when compared with the spectrum of the pre-
cursor aldehyde, there is the disappearance of the intense
stretching band characteristic of the m(C=O) bond of the
aromatic aldehyde (* 1700 cm-1). These spectra data
indicate the formation of a Schiff base from the starting
materials [16–19].
By analyzing the IR spectra of compound C.2 can be
observed the presence of the main bands of C.1, besides the
absence of the bands at 2328, 446 and 409 cm-1 assigned
to the C=N precursor [PdCl2(CH3CN)2], that indicates the
Synthesis of C.2
The C.2 compound was prepared under an inert and
anhydrous atmosphere. A dichloromethane (10.0 mL)
solution of C.1 (0.4134 g; 1.16 mmol) in dichloromethane
(30.0 mL) was added to
a stirred dichloromethane
Table 1 Results of chemical analyses of the compounds C.1–C.5
(30.0 mL) solution of [PdCl2(CH3CN)2] (0.300 g;
1.16 mmol). The mixture was stirred at room temperature
(approximately 298 K). After a magnetic stirring of the
mixture for 20 h, the solvents were evaporated and the C.2
compound was precipitated by adding pentane. The pre-
cipitate was separated by filtration, washed with ethyl ether
and dried in vacuum. Literature procedures were followed
for the synthesis of [PdCl2(CH3CN)2] using PdCl2 [15].
Yield 80%.
Compound
Carbon/%
Found
Hydrogen/%
Nitrogen/%
Calc.
Found
Calc.
Found
Calc.
C.1
C.2
C.3
C.4
C.5
67.7
45.3
42.5
44.1
48.6
67.4
45.0
41.6
43.9
48.3
6.9
5.0
4.0
4.9
4.8
6.8
4.6
4.2
4.5
4.5
7.9
5.3
7.9
5.3
5.2
4.9
20.6
9.8
20.5
10.2
123

Thermal behavior study of palladium(II) complexes containing the iminic ligand…
proton (–HC=N–) in E conformation, whereas the sign in
O
9.85 ppm refers to the same proton but in Z conformation,
related to the ligand’s (HC=N) connections. The chemical
shifts of iminic hydrogens are sensitive to conformation
effects, due to other effects such as charge density and
magnetic anisotropy. For Schiff bases of N-benzylidene
type, the chemical shift of iminic hydrogen can range from
7.56 to 9.78 ppm [25].
O
O
O
N
N
C.1
Forming coordination compounds, palladium shifts its
electron density to form a coordinative binding deshielding
even more the nearby nuclei and causing an increase in the
chemical shift of the proton (–HC=N–) from 8.19 to
8.62 ppm in the C.2, C.3 compounds and 8.39 ppm in C.4,
which have low intensities in relation to the 9.82 ppm
signals observed for C.2, C.3 and C.5 and to 9.86 ppm for
C.4. The fact that these signals ’ 9:8 ppm are more intense
than the signals at 9.62 and 9.39 ppm also confirms the
formation of the coordination compound, as the geometry
of the palladium(II) atom is a square planar, leaving it in a
position very close to the aromatic rings, which makes the
products containing the ligand in the ZZ and EZ confor-
mations more stable. This is different from the zinc and
mercury compounds, that are found in the literature with
signals between 8.22 and 8.40 ppm [19, 26], and that
contain the same C.1 ligand and halides (Br- and I-), but
which have tetrahedral geometry and retain the most
stable conformation EE of the ligand, because in these
geometrics the steric effects are minimized. The spectra for
the C.2 and C.3 compounds are very similar in relation to
the chemical shifts of protons. However, the changes in the
coupling constants (J) in both the aromatic hydrogens and
the methylenic hydrogens support the proposal of replacing
one of the chlorides by a bromide, since the chemical
environment of such protons is slightly modified. The
substitution of chloride ions by azide ions generates small
changes in the chemical shifts of the protons, referring to
the imines; from 8.62 to 8.39 ppm and from 9.82 to
9.86 ppm, which refer, respectively, to the protons of the
imine (–HC=N–) in the E and Z conformations in the
ligand. Unlike the others, C.5 has a spectrum with a
number of signals considerably smaller. The absences of
signals related to protons, assigned to the ligand with
E conformation, are consistent with the replacement of the
chloride ions by the cyanate ions, since due to the intro-
duction of this large group, the major product exhibited a
structure having the ligand in ZZ conformation. In the
aromatic H region (6.8–7.6 ppm) also, we can see signals
at different intensities, which indicate the formation of
products with different conformations and are shown in
Table 3. Products with different conformations are
observed due to the weakening of (C=N) bindings, when
palladium is coordinated with the ligand, which results in
an increase in rotation freedom [16].
O
O
O
O
N
N
P d
–
X1
X2
C.2 = X = X = Cl
1
2
–
–
C.3 = X = Br and X = Cl
1
2
–
C.4 = X = X = N
3
1
2
–
C.5 = X = X = NCO
1
2
Fig. 1 Proposed structures of the C.1–C.5 compound
formation of the [PdCl2(3,4dm-1,2am)] compound
[20, 21]. However, there was a shift in m(N=C) band to
lower frequency (1626 cm-1). It can be explained by the
interaction between the metal and the Schiff base binding
site (nitrogen atoms), where an electronic relocation occurs
in this bond [22]. The replacement of a Cl- by Br- halide
caused no distinction in the IV spectrum of the C.3 com-
pound. The terminal coordination of azide group in C.4
was suggested by the masNNN band at 2019 cm-1 [22, 23].
Concerning the IR spectrum of C.5, the presence of the
masNCO absorption at 2172 cm-1 indicated the existence of
N-cyanate groups coordinated in a terminal mode [22, 24].
The bands frequencies observed in the IR spectra for the
novel complexes and the irrespective assignments are
presented in Table 2, which allowed the elucidation of the
molecular structures.
1H and 13C NMR spectra
Chemical shifts (d) and coupling constants (J) observed in
1H NMR spectra, Fig. 2, of the C.1 ligand and the C.2–C.5
complexes, are shown in Table 3, where the values in bold
correspond to the more intense signals related to the
compounds with more stable E/Z conformation and,
therefore, the major product. In the 8–10 ppm region for
C.1, a strong signal is noted in 8.19 ppm referring to the
123

T. T. Xavier et al.
Table 2 Assignments of the
principal bands presents in IR
spectrum of C.1–C.5
compounds
Assignments
Wavenumber/cm-1
C.1
C.2
C.3
C.4
C.5
m(C–H) Aryl C(sp2)
mas(C–H) C(sp3)
mas(C–H) (–CH2–)
ms(C–H) C(sp3)
ms(C–H) (–CH2–)
mas(NNN)
3003 (w)
2945 (w)
2912 (w)
2894 (w)
2833 (w)
–
2999 (w)
2956 (w)
2936 (w)
–
3003 (w)
2957 (w)
2933 (w)
–
2999 (w)
2957 (w)
2934 (w)
–
2999 (w)
2957 (w)
2936 (w)
–
2837 (w)
–
2835 (w)
–
2838 (w)
2019 (s)
–
2837 (w)
mas(NCO)
–
–
–
2172 (w)
1632 (m)
1593 (s)
1460 (m)
1421 (m)
1275 (s)
1018 (s)
854 (w)
810 (m)
m(C=N) Arylimine
m(C=C) Aryl
1637 (s)
1583 (s)
1458 (s)
1421 (s)
1267 (s)
1022 (s)
874 (w)
810 (m)
1626 (m)
1595 (s)
1458 (m)
1421 (m)
1273 (s)
1018 (s)
854 (w)
810 (m)
1628 (m)
1595 (s)
1460 (m)
1421 (m)
1273 (s)
1018 (s)
854 (w)
808 (m)
1626 (m)
1593 (s)
1460 (m)
1421 (m)
1273 (s)
1016 (s)
854 (w)
808 (m)
m(C=C) Aryl
mas(C–O–C)
ms(C–O–C)
dsc(C–H) Aryl
(s) strong, (m) medium, (w) weak, s symmetric, as asymmetric, m axial deformation, d angular deformation,
c out-of-plane deformation
C.5
C.4
C.3
C.2
C.1
11
10
9
8
4.0
3.9
3.8
/ppm
3.7
3.6
7.55
7.45
7.35
7.25
7.15
7.05
6.95
6.85
δ
δ
/ppm
δ
/ppm
Fig. 2 1H NMR spectra for compounds C.1 and C.4 in CDCl3 and C.2, C.3 and C.5 in DMSO-d6
The data for the NMR spectra of the 13C to C.1–C.5,
Fig. 3, indicate the formation of coordination compounds.
In the 162–192 ppm region, the signal appears at
162.19 ppm in C.1, shifting to 168.95 ppm (C.2), 168.95
and 170.07 ppm (C.3), 167.29 ppm (C.5), with very low
intensities that are referring to the (–HC=N–) C in the E
conformation, and the most intense signals in 191.85 ppm
(C.2, C.3 and C.5) 190.93 ppm (C.4) assigned to the
iminic carbons in the Z conformation. The 13C NMR
spectrum shows many signals close to the values assigned
to the ligand C.1, Table 4, in the aromatic carbons region
and the 45–65 ppm region, referring to the carbons (–O–
CH3) and (–NCH2–) groups, which contribute to the
interpretation of mixtures of products with different con-
formations (EE, ZZ, ZE). Thus, as it is shown in Fig. 3,
there are signals, in the C.2, C.3 compounds, related to the
123

Thermal behavior study of palladium(II) complexes containing the iminic ligand…
Table 3 1H NMR data (ppm)
Assignment
C.1
C.2
C.3
for compounds C.1 and C.4 in
CDCl3 C.2, C.3 and C.5 in
DMSO-d6, given as d (ppm) and
multiplicity-J (Hz)
d/ppm
J/Hz
d/ppm
J/Hz
d/ppm
J/Hz
–O–CH3 (A)
–NCH2– (B)
Ar–H (C)
3.90
3.93
6.85
7.08
7.38
8.18
6.98
7.46
7.40
9.84
s
3.85
3.81
7.09
7.28
7.22
8.62
7.15
7.53
7.36
9.82
s
3.85
3.81
7.09
7.28
7.22
8.62
7.15
7.54
7.37
9.82
S
dd-13.9; 6.1
d-8.3
t-4.36
t-3.82
d-8.46
d-8.42
Ar–H (D)
dd-1.9; 8.2
d-1.86
dd-1.45; 8.30;
dd-1.69; 8.42;
Ar–H (E)
d-1.46
1.68
–HC=N– (F)
Ar–H (C0)
Ar–H (D0)
Ar–H (E0)
–HC=N– (F0)
s
s
S
d-8.15
d-8.25
d-8.25
dd-1.87; 8.15;
d-1.94
dd-1.82; 8.22;
dd-1.89; 8.25;
d-1.74
d-1.84
s
s
S
Assignment
C.4
C.5
Conformations (EE. ZZ e ZE)
d/ppm
J/Hz
d/ppm
J/Hz
–O–CH3 (A)
–NCH2– (B)
Ar–H (C)
3.96
m
3.83
m
6.92
7.12
7.02
8.39
6.98
7.46
7.41
9.86
d-8.45
–
–
Ar–H (D)
dd-1.92; 8.28;
–
–
Ar–H (E)
d-1.96
–
–
–HC=N– (F)
Ar–H (C0)
Ar–H (D0)
Ar–H (E0)
–HC=N– (F0)
s
–
–
d-8.17
7.15
7.54
7.37
9.82
d-8.23
dd-1.90; 8.17;
dd-1.86; 8.23;
d-1.85
d-1.86
s
s
The values in bold correspond to the more intense signals that can be observed in Fig. 2
1H nuclei of the (–NCH2–) group, more shielded, compared
to the same cores in the C.1 and C.4 compounds, in Fig. 3
also, we can observe more shielded signals ’ 47 ppm
related to the 13C nuclei of this group (–NCH2–).
relationship between TG curves and DTA peaks was
observed, respectively.
As it can be observed from the TG curve shown in
Fig. 4, the C.2 compound is thermally stable up to 396 K.
Within the range from 396 to 817 K, a mass loss is
observed, referring to the elimination of 3,4dm-1,2am and
Cl- ligands. The DTA curve shows three exothermic
peaks, at 571, 645 and 794 K, related to this loss. However,
before the elimination of the ligands is finished, the oxi-
dizing of Pd0 to PdO is starting, causing a mass gain up to
1082 K, concerning the incorporation of 0.5 O2
(396–1082 K experimental Dm: 73.72%/calculated Dm:
- 77.06%). The mass loss of 3.37% initiated at 1082 K
shown in the TG curve (Dm calculated: - 3.00%), together
with an endothermic peak at 1101 K shown in the DTA
curve, indicates the reduction in palladium(II) oxide in
metallic palladium (PdO ? Pd0) eliminating 0.5 O2.
Thermal analysis
TG curve of organic compound C.1 shows that it is ther-
mally stable up to 449 K. After this temperature is
exceeded, the compound begins to decompose, occurring
mass lost up to 1060 K. Being an organic compound, no
formation of residue is observed. It is possible to identify
an endothermic peak of 433 K in the DTA curve, typical to
the physical phenomenon, which corresponds to the melt-
ing point of the compound that is why we did not observe
any mass change. These data are consistent with the values
obtained from the melting point equipment (* 428 K). A
123

T. T. Xavier et al.
(i)
(h)
(g)
(f)
(e)
(d)
(c)
(b)
(a)
200
190
180
170
160
150
140
130
120
110
100
90
80
70
60
50
δ
/ppm
Fig. 3 NMR spectra for compounds C.1–C.5: (a) 13C{1H} of C.1 in
CDCl3; (b) 13C/DEPT-135 of C.1 in CDCl3; (c) 13C/DEPT-90 of C.1
in CDCl3; (d) 13C{1H} of C.2 in DMSO-d6; (e) 13C/DEPT-135 of C.2
in DMSO-d6; (f) 13C/DEPT-90 of C.2 in DMSO-d6; (g) 13C{1H} of
C.3 in DMSO-d6; (h) 13C{1H} of C.4 in CDCl3 e; (i) 13C{1H} of C.5
in DMSO-d6
Table 4 13C/DEPT NMR data
(ppm) for compound C.1 in
Carbon
13C d/ppm
13C/DEPT-135
13C/DEPT-90
Assignment
CDCl3, given as d (ppm)
a
55.91
64.64
55.91
b
64.64 (invert)
108.66
c or d
108.66
110.35
123.06
129.41
149.27
151.30
162.19
108.66
110.35
123.06
110.35
e
f
123.06
g
h
i
162.19
162.19
This thermal behavior is repeated in compounds C.3,
C.4 and C.5, with variations in the initial and final
decomposition temperatures, in the mass variation in each
step and in the final residue percentage. These final resi-
dues were analyzed by X-ray diffraction powder, and peaks
were identified on the basis of ICDD to metallic palladium
(05-0681) and palladium(II) oxide (06-0515) [27]. The data
obtained in the TG/DTA curves are in Table 5.
decomposition of the azide ion is one of the factors that
may justify the differences in the TG curve of C.4. It is
interesting to note that the substitution of Cl ions by Br and
pseudohalides (N3 and NCO) caused a change in the final
decomposition
temperature:
C.3
(904 K) [ C.2
(817 K) [ C.5 (789 K) [ C.4 (771 K). Compound C.3
showed higher final temperature. This may be explained by
the higher affinity of the Br ion for Pd(II), according to the
theory of acidity and basicity of Pearson [28], resulting in a
greater bond stability, thereby increasing the final tem-
perature of the decomposition step. In TG curves of the
On analyzing the TG curves of all synthesized com-
plexes (Fig. 5), the C.2, C.3 and C.5 compounds show very
similar decomposition patterns. The relative ease of
123

Thermal behavior study of palladium(II) complexes containing the iminic ligand…
15.0
12.5
10.0
7.5
gain, concerning the oxidation of palladium, that occurs
simultaneously with the losses referring to the elimination
of organic compounds, halides and pseudohalides, and
afterward, a mass loss above 1073 K which is accompanied
by an endothermic peak in the DTA, due to the formation
of palladium(II) oxide followed by their reduction into
metallic palladium.
C.2
(a)
(b)
100
TG
DTA
(a)
EXO up
80
60
5.0
The TG and DTA curves of the PdCl2 compound, sup-
plied by VetecÒ, are shown in Fig. 7, where we can see a
similar behavior. The thermal decomposition starts at
approximately 820 K. In the range from 820 to 1079 K,
there is a mass loss of 32.82% equivalent to the elimination
of the chloride ligands and the capture of 0.5 O2 due to the
formation of palladium(II) oxide (calculated Dm:
- 31.64%). Note that, in this case, the 0.5 O2 incorporation
occurs completely simultaneously with the 2 Cl-elimina-
tion, because the PdCl2 compound decomposes at higher
temperatures compared to the C.2–C.5 compounds. In the
range from 1079 to 1176 K, another mass loss occurs with
a value of 8.14% equivalent to the reduction of the formed
palladium(II) oxide (calculated Dm: - 8.36%). The
58.76% existing residue is within the instrumental error of
3% (calculated 60.01%). The data of the TG and DTA
curves of PdCl2 are also in Table 5.
40
20
2.5
(b)
0.0
0
– 2.5
400
600
800
1000
1200
Temperature/K
Fig. 4 TG e DTA curves of the complex C.2
complexes, a very slight initial mass loss is observed, most
possible due to solvent evaporation.
The DTA curves of the synthesized palladium com-
plexes, shown in Fig. 6, offer data that agree with TG
curves. The amount of energy released in the C.4 decom-
position was higher than that of the other. This thermal
behavior similar to that observed for other Pd(II) com-
pounds containing coordinated azide exhibits inherent
tendency of highly exothermic decomposition, yielding Pd
and/or PdO and gaseous products, such as N2. In some
cases, these compounds are potential explosives [29, 30].
Analyzing the TG and DTA curves of all the compounds
that contain palladium, we can see the presence of mass
The formation of solid oxides, through heating, that
contain platinum group metals has been studied for several
years; Bayler and Wiedemann published a study in 1975
[31] in which they confirm the palladium(II) oxide for-
mation and its thermal decomposition during the heating
Table 5 Thermal analysis data of compounds C.2–C.5 and PdCl2
Compounds
Step
DT/K
Dm/%
DTA peaks/K
Exo.
Assignment
Obt.
Calc.
End.
C.2
1
396–1082
- 73.72
- 77.06
571
- 2Cl-, –(3,4dm-1,2am)
645/794
? 0.5 O2
2
1082–1351
- 3.37
22.44
- 3.00
19.94
1101
1093
- 0.5 O2
Pd0
Residue
C.3
C.4
1
391–1070
- 74.96
- 2.89
21.49
- 78.84
- 2.75
18.41
575/701/869
–Br-, –Cl-, –(3,4dm-1,2am), ? 0.5 O2
2
1070–1355
- 0.5 O2
Pd0
- 2(N3-), –(3,4dm-1,2am)
Residue
1
371–1081
- 76.23
- 77.58
500/667
744
? 0.5 O2
2
1081–1446
- 3.00
20.58
- 2.93
19.46
1096
1104
- 0.5 O2
Pd0
Residue
C.5
1
397–1088
- 74.53
- 3.35
21.30
- 77.6
- 2.03
19.46
574/644/767
- 2CNO-, -(3,4dm-1,2am), ? 0.5 O2
2
1088–1350
- 0.5 O2
Pd0
Residue
PdCl2
1
820–1079
- 32.82
- 8.14
58.76
- 31.64
- 8.36
60.01
691/961
1102
- 2Cl-, ? 0.5 O2
- 0.5 O2
Pd0
2
1079–1176
Residue
123

T. T. Xavier et al.
treatment of palladium metallic samples. The first traces of
palladium(II) oxide are formed at 473 K, the oxidation is
complete at about 973 K, and its decomposition follows in
the range from 1093 to 1123 K. Moreover, they concluded
that the temperatures at which these events occur will vary
according to the grain size of the metallic powder, the b
and the ovens atmosphere.
100
80
(a)
(b)
(c)
(d)
C.2
C.3
C.4
C.5
(c)
EXO up
60
In the present work, the thermal analysis for metallic
palladium, supplied by Sigma-AldrichÒ, was carried out
under the same b (20 K min-1) and atmosphere (synthetic
air) conditions as those performed for the obtained C.2–C.5
compounds, as well as in nitrogen atmosphere. These data
are shown in Fig. 8. As expected, and according to data
from literature [28], the TG and DTA curves of metallic
palladium in synthetic air show a mass gain, indicating that
part of the metallic palladium had oxidized and then
reduced, according to its mass loss at temperatures around
1073 K, as well as the presence of the endothermic peak at
1091 K in the DTA. These events are not observed in the
metallic palladium TG and DTA curves in the N2 atmo-
sphere, since without the presence of O2, palladium(II)
oxide formation is not possible.
(d)
40
20
(a)
(b)
400
600
800
1000
1200
Temperature/K
Fig. 5 TG curves of the complex C.2–C.5
(c)
(a)
C.2
C.3
C.4
C.5
25
(b)
(c)
(d)
20
EXO up
(d)
15
Conclusions
(a)
10
The 3,4dm-1,2am ligand C.1 and the [Pd(Cl)2(3,4dm-
1,2am)]
(C2),
[PdBrCl(3,4dm-1,2am)]
(C.3),
(b)
5
0
[Pd(N3)2(3,4dm-1,2am)] (C.4) and [Pd(NCO)2(3,4dm-
1,2am)] (C.5) compounds were synthesized and charac-
terized by elemental and thermal analysis and IR spec-
trometry as well as by 1H and 13C NMR. These data
complement each other and agree with the presented
structures. The C.3 compound, despite being synthesized
as the others, in molar ratios (1:2, C.2/KBr), the elemental
400
800
1000
1200
600
Temperature/K
Fig. 6 DTA curves of the complex C.2–C.5
Pd0
1.5
1.5
1.0
0.5
0.0
108
Synthetic air
(a)
(b)
TG
DTA
PdCl2
(a)
(b)
1.0
100
105
102
TG
DTA
(a)
EXO up
0.5
(b)
EXO up
0.0
90
80
70
60
(b)
99
(a)
– 0.5
400
600
800
1000
1200
Temperature/K
Pd0
– 0.5
– 1.0
1.5
108
Nitrogen
(a)
(b)
TG
1.0
DTA
105
102
(b)
EXO up
0.5
0.0
– 1.5
(a)
99
– 0.5
400
800
1000
1200
600
400
600
800
1000
1200
Temperature/K
Temperature/K
Fig. 7 TG e DTA curves of the complex PdCl2
Fig. 8 TG e DTA curves of the Pd0 in synthetic air and nitrogen
123

Thermal behavior study of palladium(II) complexes containing the iminic ligand…
14. Akerdi SJ, Grivani G, Stoeckli-Evans H, Khalaji AD. Crystal
and thermal analyses show consistent results with the
replacement of only one Cl-. From the final decomposition
temperatures, the thermal stability of the complexes can be
ordered in the following sequence: C.3 > C.2 > C.5 >
C.4. Thermal analysis data also showed that occurs for-
mation of palladium (II) oxide with heat treatment for all
C.2–C.5 compounds, including PdCl2 reagent and palla-
dium metal, occurs and reducion to palladium metalic at
temperatures close to of 1093 K.
structure of dinuclear azide-bridged copper(II) complex
[Cu2((3,4-MeO-Ba)2En)2(l1,1–N3)2(N3)2]{(3,4-MeO–Ba)2
En=N,N0-bis(3,4-dimethoxybenzylidene)-1,2-ethanediamine}.
Russ J Coord Chem. 2011;37:394–8.
15. Bego AM, Frem RCG, Netto AVG, Mauro AE, Ananias SR,
Carlos IZ, da Rocha MC. Immunomodulatory effects of Palla-
dium(II) complexes of 1,2,4-triazole on murine peritoneal mac-
rophages. J Braz Chem Soc. 2009;20:437–44.
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electronic effects on E/Z composition of exocyclic cyclopalla-
dated N-benzylideneamines. J Organmet Chem. 1997;545:131–7.
17. Bandyopadhyay D, Layek M, Fleck M, Saha R, Rizzoli C.
Synthesis, crystal structure and antibacterial activity of azido
complexes of cobalt(III) containing heteroaromatic Schiff bases.
Inorg Chim Acta. 2017;461:174–82.
18. Aranha PE, Santos MP, Romera S, Dockal ER. Synthesis, char-
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chromium(III) complexes. Polyhedron. 2007;26:1379–82.
19. Khalajia AD, Grivan G, Rezaei M, Fejfarova K, Dusekc M.
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Acknowledgements We would like to thank CAPES, CNPq, FINEP
and FAPEMIG for financial support (Project: CEX - APQ-01984-14).
This work is also a collaboration research project of a member of the
´
Rede Mineira de Quımica (RQ-MG) supported by FAPEMIG (Pro-
ject: REDE-113/10).
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